It has been observed that pellets, specially of larger sizes such as L.G,and S.G.(Buck shots), often carry identifiable markings These are scratched by the surface irregularities of the barrel. The pellets carrying these markings can be identified provided such markings can be produced on test specimens. However, statistical probabilities are very small that other shots fired through the same barrel would touch exactly identical points every time. Due to difficulties in obtaining desired test specimens, the identification of fired pellets remained impracticable. Identification of such pellets should be possible if the markings from the requisite points area could be reproduced. A successful attempt has been made to obtain such test specimens, with special reference to smooth bore short barreled country made pistols chambered for 12 bore cartridges.
THEORY It is well known that barrels are not perfectly smooth and their surfaces are irregular, having rough spots of elevations and depressions. The striations on pellets are produced by their passage over these surface irregularities and they are highly characteristic for individualization. The pellets may be scratched only by a small portion of the barrel. Normally only one sides of the pellets is found to have striations which are due to the scratching by one segment of the barrel. These markings from the required surface can be ensured if the striations due to the entire surface of the barrel are obtained.
A projectile may carry striations due to the entire surface irregularities if it perfectly seals the bore. Perfect sealing of the bore can very well be achieved by using projectile of greater diameter than that of the bore. But shotgun cartridges are not loaded with any single projectile having diameter greater than the respective bore diameter. Amongst the available single shotgun projectiles, single balls can alone be considered to serve the purpose. But single ball diameter is always less than the minimum permissible diameter of the bore of the gun. Therefore, single balls of larger diameter can only be used for test firing It is not possible however to do this because of limitations of chamber size and possibility of bursting of the barrel. Single balls of slightly larger diameter can, however, be pushed through the barrel so as to take on the necessary bore markings for comparison. But a single ball being spherical has another disadvantage of minimum surface contact and is also not commercially available in different sizes according to the requirement. Considering the above factors, the best suited test specimen should be cylindrical in shape and be made from lead, which being soft can be pushed through the barrel with ease. It is, therefore, clear from the aforesaid discussion that, for comparison, test specimen of lead, cylindrical in shape and slightly greater than bore diameter, should be pushed through the barrel. This test specimen will necessarily touch the entire inside surface of the barrel and will also bear markings from the set of points of particular interest.
EXPERIMENTATION Cylindrical lead specimen of desired dimension can very easily be made by casting. An improvised method has been devised and adopted in the laboratory for preparing such test specimens. A flexible steel strip of 3/4" width has been used which could be turned to form a cylinder of any desired diameter. Lead cast can be prepared by pouring molten lead pellets. The steel strp and the cylindrical lead specimen cast in it are shown in Figure I
FIGURE I
Experimental firings were conducted through a country made pistol chambered for 12 bore cartridges , using 12 bore cartridges loaded with LG(Buck)shots. The fired shots were recovered. Two pellets, out of six, were found to carry sufficient striations for comparison. Test lead specimens of slightly greater than bore diameter were prepared by adopting aforesaid method. Two such test specimens were pushed through the barrel of the country made pistol. As expected, the bore markings on both the test specimens matched throughout. Thereafter, one of the recovered fired pellets and the test specimen were compared for characteristic bore markings. On thorough examination, positive match was observed, proving thereby that the striations which matched on the test specimen and fired pellet were due to the same source. Figure II shows a positive match between test and recovered fired pellet.
FIGURE II
The other pellet having sufficient striations also matched with the tests. However, as expected, the position of matching was entirely different from the previous one.
J. K. Sinha.
Identification of projectiles fired from smoothbore, improvised
and home made firearms-- Author's Ph.D.thesis
**Part of a chapter of thesis-- Brief description**
The procedure of obtaining tests by pushing lead slugs of larger diameter pose manifold problems. Therefore, firing of slugs of larger diameter is the only plausible solution. To achieve the objective, uncupped paper shotgun cartridge is used for test purposes. After removing the top shot wad and the shot charge, lead cast of suitable width is made in the emptied portion by pouring molten lead, keeping the outer wall of the cartridge wrapped with cotton soaked in water. These cartridges are used for test purposes. Lead slugs are fired as projectile in bullet recovery box and fired slugs are recovered. The fired slugs carry barrel contact marks around the entire periphery. The fired slugs are examined inter-se under a comparison microscope and then compared with the questioned fired pellet to establish linkage. Striation matching of barrel marks on LG (Buck shot) with lead slug fired from 12 bore country made pistol (M.D .69") is shown in Fig. III
FIGURE III